Distinguished honors bestowed on members of the LBL scientific staff dur ing July through November 1991 include the following:
Glenn T. Seaborg, associate director at large at LBL and University Professor at the University of California, received the National Medal of Scienc e in September 1991. He was cited for his outstanding work as a nuclear chemist and as a teacher. The Medal of Science, the nation's highest award for scientifi c achievement, was the latest of numerous awards that Seaborg has won over the y ears. In 1951, he shared the Nobel Prize in Chemistry with the late Edwin McMill an for work on the chemistry of the transuranium elements, a field that still ho lds his interest.
John Newman,a researcher in LBL's Chemical Sciences Division and pro fessor in UC Berkeley's Department of Chemical Engineering, was awarded the 1991 Olin Palladium Medal by the Electrochemical Society, Inc., for his contribution s to electrochemical science and technology.
Morton Denn of LBL's Center for Advanced Materials and UCB's D epartment of Chemical Engineering, was named a Fellow of the American Institute of Chemical Engineers for his "outstanding work as an educator and researcher in polymer processing and rheology, as well as fluid mechanics, reaction engineeri ng, and process optimization and control."
Miklos Gyulassyof the Nuclear Science Division was elected a Fellow of the American Physical Society in recognition of his "innovative work on the s pace-time aspects of nuclear collision dynamics, pion interferometry, quark-gluo n plasma formation and hadronization in relativistic and ultra-relativistic nucl ear collisions."
Wladyslaw Swiatecki of the Nuclear Science Division was awarde d the Polish Physical Society's Marian Smoluchowski Medal for his outstanding co ntributions to science and to development of international scientific cooperatio n. The medal is the highest scientific distinction granted by the society.
Erik Anderson of the Center for X-ray Optics was a member of a team th at won a 1991 R&D-100 Award for the development of a high-resolution scanning ph otoelectron microscope. The awards go to Research and Development magazine's cho ices for the year's top 100 achievements in technology.
Gareth Thomas, scientific director of the National Center for Electr on Microscopy, received the 1991 Albert Sauveur Achievement Award from the Ameri can Society for Materials. He was cited for his "pioneering efforts in the devel opment and applications of electron microscopy and for fostering the universal a cceptance of this technique in the evolution of modern materials science."
Thomas Budinger, director of LBL's Research Medicine and Radiatio n Biophysics Division, received the 1991 Distinguished Scientist Award from the Society of Nuclear Medicine. The award recognizes Budinger's "distinguished cont ributions to nuclear medicine."
Dariush Arasteh, Brent Griffith, and Steve Selkowitz of the Energ y and Environment Division were recognized by the magazine Popular Science for t heir work in developing a new gas-filled panel insulating material. The material was chosen as the year's best new product in the home technology arena and was one of 10 grand winners on the magazine's list of the 100 best new products and inventions of 1991.
Patents were awarded recently for inventions by these LBL researchers:
Tim Renner, Mark Nyman, and Ronald Stradtner for an ionization chamb er dosimeter for measuring the radiation dose delivered to a patient; and Ste ve Selkowitz for a thermal insulated glazing unit.
The first step in the chemical process that enables the eye to detect light h as been time-resolved by a team of LBL and UC Berkeley scientists. This reaction , which takes place within 200 millionths of a billionth of a second, is believe d to be the fastest ever measured.
LBL's Robert Schoenlein and Charles V. Shank, and UCB's Linda Peteanu an d Richard Mathies used strobelike flashes of blue-green laser light to stop the action on the twisting of a chemical bond that triggers the process of sight. Th e bond is between carbon atoms m a protein called rhodopsin, the main constituen t of the rod and cone cells in the eye's retina.
"Our observations have important implications for the development of suc h things as artificial vision or solar converters," Mathies says. "In order to c ontrol a chemical reaction and dictate its outcome, we must first understand its dynamics."
Vision starts when photons of light enter the eye and are focused onto t he retina. Absorbing the energy of even one photon causes a specific carbon-carb on double bond within the rhodopsin molecule to twist a full 180 degrees. Like a key unlocking a door, the twisting of the bond opens the way for converting pho tons into signals that are transmitted via the optic nerve to the brain for inte rpretation.
Scientists have long known that the twisting or "isomerizing" of the rho dopsin molecule is the primary step in vision but, until now, did not know how q uickly it takes place. The LBL-UCB team was able to record-in a sequence of spec tral snapshots-the entire reaction from start to finish using laser spectroscopy techniques they developed that operate on a femtosecond time scale. (A femtosec ond is a millionth of a billionth of second.)
The LBL-UCB team obtained their measurements working with samples of rhodopsin extracted from cow retinas. First, a unique blue- green laser beam tha t flashed in pulses of only 35 femtoseconds duration was used to "pump" rhodopsi n with the energy needed to make it twist. A second beam, with a broader spectru m and pulse length of only 10 femtoseconds, was then used to measure the spectra l absorption patterns of the molecule as it changed shape.
Says Schoenlein, "In its original form, rhodopsin absorbs mostly green l ight. However, as it twists, the molecule starts to absorb light which is more i n the yellow and red parts of the spectrum. By measuring the changes in the colo rs absorbed by the molecule, we can tell how fast the molecule is isomerizing."
The speed of rhodopsin's isomerization is considerably faster than anyon e expected and helps explain why the eye is so efficient at collecting light.
"The energy of a photon is converted to mechanical motion so quickly tha t there is no time for any energy to dissipate or leak away," Schoenlein says. " As a result, the vision system is so sensitive that under ideal conditions it ca n detect a single photon."
Rhodopsin's light- sensitive region, called the "chromophore," is a form of vitamin A, consisting of a chain of carbon atoms. The twisting takes place a t a double bond between the 11th and 12th carbon atoms in the chain, transformin g the chromophore from what is called an "11-cis" configuration to what is calle d an "all-trans" configuration. This change in the chromophore leads to a change in shape of the rhodopsin molecule that initiates a cascade of enzymatic events which excite the retinal rod cell.
Says Mathies, "If the transformation of the chromophore did not take pla ce as fast as it does, competing processes would prevent the detection of light. As it is, generally about two-thirds of the incoming photons are converted to r eactions that yield the all-trans photoproduct."
The isomerization of rhodopsin is irreversible. After the protein change s shape, it eventually loses its retinal chromophore. The eye must then construc t a new protein using part of the old molecule and a fresh supply of 11-cis vita min A. This is why vitamin A deficiency reduces the eye's ability to detect ligh t.
The next step in this research, the team says, will be to study the twis ting reaction when the rhodopsin or the vitamin A chromophore has been modified. This, they say, will help them to better understand how and why the mechanism w orks, which, in turn, may provide clues for making light detectors and photon sw itches that could be used in photosensors, biological solar energy converters, a nd optical computers.